The present invention relates to a method of producing an instrument panel of a motor vehicle or similar molding of foamed resin capable of fitting electrical parts thereon as desired. More particularly, the present invention is concerned with a method of producing a molding of foamed resin in which a flexible printed circuit (FPC), which is electrically connectable to electrical parts, is buried.
In a motor vehicle, for example, an instrument panel is loaded with a combination meter which is the combination of various kinds of meters such as a speedometer, warning lamps, etc. Also mounted on the instrument panel are a heater control switch, a cruise control switch and other various switches, a cigarette lighter, a radio, and so on. A prerequisite of an instrument panel is therefore that it be provided with exclusive sections for fitting such electrical parts.
Each electrical part fitting section stated above usually includes a coupler for receiving an electrical part therein. When an electrical part is inserted in the coupler, electrical connection of the electrical part to a power supply or the like is established. Wirings are laid in the individual fitting sections and each has terminals which are disposed in the interior of the associated coupler.
An instrument panel has to be provided with a number of such fitting sections for electrical parts, and a wiring has to be provided in each of the fitting sections. Efficient wiring may therefore be promoted by using an FPC which is extremely thin and easy to deform. More specifically, an FPC consists of a pair of resin films and a lead circuit which is configured by etching copper foil or similar metal foil and sandwiched between the resin films. The FPC not only allows a number of leads to be collectively formed in a single sheet but also readily adapts itself to any complicated surface configuration such as the surface of an instrument panel, promoting the ease of wiring work.
An instrument panel has customarily been implemented as a laminate having three layers, i.e., a covering made of soft resin, a base made of ABS resin or similar hard resin, and a padding made of foamed urethane or similar foaming resin and sandwiched between the covering and the base. An FPC and couplers are each mounted on the base by using adhesive or screws. Such a prior art three-layer instrument panel, however, is not satisfactory because the base and the padding have to be produced independently of each other and then bonded together, resulting in a disproportionate production cost.
In the light of this, even the base may be formed from a foamed resin and molded integrally with the padding. A question arising here is how to mount the FPC and couplers on the instrument panel. Specifically, when the base is made of foamed resin, it is impossible to fit the electrical parts on the base by an using screws. Even if such fitting is implemented by adhesive, the electrical parts easily come off because the base made of the foamed resin is elastic. Further, the adhesive scheme is not effective to sufficiently cut down the production cost because the adhesion has to be performed after the whole instrument panel has been molded.
In the case that parts in general are fitted on a molding of foamed resin which includes a base of foamed resin, they may be buried in the base to be molded integrally with the base. It may therefore be contemplated to bury an FPC and couplers in the base of an instrument panel which is made of foamed resin when the latter is molded. This not only eliminates the need for the adhesion otherwise performed after molding but also protects the FPC from damage during the transport, assembly or the like of the instrument panel because it is accommodated in the base.
Any electrical part may be buried in a base of foamed resin simply by positioning it in a metal mold and then pouring an undiluted solution of foaming resin in the metal mold and causing it to foam and solidify. However, since the FPC to be buried in the base is in the form of a thin flexible sheet, the FPC simply positioned in the metal mold is apt to deform due to pressures ascribable to the solution which is poured and caused to foam. When so deformed, the FPC and therefore its terminals are brought out of their predetermined positions and fail to make electrical contact with an electrical part.
A further prerequisite of a coupler is that it be exposed to the outside on the front side of a molding of foamed resin in order to allow an electrical part to mate with the coupler. While this prerequisite may be met by shaving off the base after the molding has been produced so as uncover the inner walls of the coupler, this kind of approach not only makes it necessary to machine the molding produced but also brings about a fear that the terminals of the FPC disposed in the coupler are cut off when the base is shaved off. Preferably, therefore, an opening contiguous with the interior of the coupler should be formed through the base for receiving an electrical part in the event of molding the base. However, should the foaming resin be admitted into the coupler to stick to the terminals of the FPC, the resin would disturb the contact of the coupler with an electrical part because it is electrically insulative. For this reason, the interior of the coupler should be completely sealed from the exterior.